Mobile offshore drilling and production platform

ABSTRACT

The present invention relates to a mobile offshore oil drilling and production platform ( 10 ) that allows a field operator to cope with uncertainty and economically develop a small or marginal oil filed typically located in a remote location. More particularly, the invention relates to a versatile platform which includes a hull ( 12 ) extending above the level of sea to house hydrocarbon extracting and scale up or scale down hydrocarbon processing system modules and equipment with provisions to drill new wells and work-overs using modular portable vertical drilling rigs or conventional rigs, connected to a mat acting as the foundation resting on the seabed which may or may not incorporate storage, using tubular legs, and provision to even abandon the field with minimal costs and disruption. The present invention also relates to a method of installing and de-installing the oil drilling and production platform ( 10 ).

FIELD OF INVENTION

The present invention relates to a mobile offshore oil drilling andproduction platform.

BACKGROUND OF INVENTION

The world's high energy demand has driven oil prices to unprecedentedheights and put pressure on industry to produce more. Threshold levelsfor previously considered small or marginal fields have been lowered. Asmall or marginal field can be defined as a field that may not produceenough net income to make it worth developing at a given time; dependentupon a combination of technical, commercial, regulatory, productionsharing terms and also company's own Internal Rate of Return.

High oil prices however brings with it new challenges. Development costshave been pushed to new highs. Competition for the same resources fore.g. skilled manpower, specialized plant and equipment and space infabrication yards have also resulted in resource constraints. Typicallythese unexploited fields are often located in remote locations withlittle or no infrastructure. The biggest challenge, typicallyencountered in exploiting small or marginal fields are often due touncertainty as it is often impossible to predict with certainty theamount or composition of recoverable oil in place. Consequentlyplatforms have been over or under designed resulting in technicians,tools and equipment transported to site to carry out costlymodifications.

Conventional offshore platforms are built from components that aretransported separately from fabrication sites to offshore sites wherethey are put together utilizing barge mounted heavy lift cranes and/orjack-up drilling rig mounted derricks.

Due to the shortage of such crane barges and jack-up rigs, themobilization or demobilization costs and day rates for these units haveincreased. Installation of platforms to extract hydrocarbons at smalland marginal fields is no longer economically viable mainly due to thisescalation in costs.

This led to the invention of self-installing platforms called MobileOffshore Production Unit (MOPU) which can easily be re-locatable withoutthe need for a derrick barge or a jack-up drilling rig. The MOPU is usedadjacent to a wellhead platform that supports drilling operation.Hydrocarbons extracted via the wellhead platform are sent to the MOPUfor separation and further conditioning before being returned to thewellhead platform for onward transportation to a pipeline network or aFloating Storage and Offloading (FSO) vessel.

The MOPU can only be operational where a pre-installed wellhead platformwith risers linked to a pipeline network or if an FSO is present. Formarginal fields and medium sized fields in remote locations where apipeline network is non-existent, the high costs associated with theinstallation and de-installation of the wellhead platform and an FSOwill not make the project economically viable.

Therefore, there is a need for the MOPU to be made versatile for use atsmall and marginal fields with solutions to overcome uncertainty andhigh costs associated with the installation of wellhead platforms fordrilling and FSO for storage.

SUMMARY OF THE PRESENT INVENTION

Accordingly, there is provided a mobile offshore oil drilling andproduction platform wherein the platform includes a hull and a mat,wherein the mat is connected to at least one connecting legsubstantially vertical upstanding from the mat to the hull and the matincludes at least one ballast compartment to be filled with sea water orcompressed air in the platform characterized in that a drilling templateattached to the hull and mat by connecting means wherein a drillingtemplate is removeably attached to the hull and mat and the at least oneconnecting leg is provided with at least a stiffener, wherein the loadof the platform is transferred over a substantially large area of themat and then to seabed.

Also provided is a method of installing the mobile offshore oil drillingand production platform, wherein the method includes the steps ofadjusting ballast levels in the hull and the mat's ballast chambers toachieve all required conditions for the platform to be towed to anoffshore installation site, securing parts of the platform such as thelegs and caisson by securing means such as sea-fastening for the tow,towing the platform to the site, removing the securing means such asseafastening, adjusting the ballast levels to achieve all requiredconditions, activating the heightening means so that the mat, legs andthe caisson or the conductor subsea support frame to be lowered fromunderneath the hull to the seabed, de-activating a subsea clamp holdingthe caisson to the mat, to allow the caisson to self-penetrate,re-activating the clamp to provide lateral support for the caisson,fully de-ballasting the hull and activating the heightening means toelevate the hull to a desired height.

Furthermore, there is also provided a method of de-installing the mobileoffshore oil production and processing platform, wherein the method ofde-installing includes the steps of securing the wellhead deck to thecaisson or conductors by a securing means, detaching the drillingtemplate from the hull, de-activating a subsea clamp holding the caissonor the securing means to release the conductor subsea support frame fromthe mat, activating the heightening means so that the hull is lowered tosubstantially the sea level, removing any adhesion caused by soil-inareas surrounding the mat, activating the heightening means so that themat and the legs are returned from the sea-bed to underneath thefloating hull, and re-adjusting the platform to required conditions fortowing to the next destination.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be fully understood from the detaileddescription given herein below and the accompanying drawings which aregiven by way of illustration only, and thus are not limitative of thepresent invention, wherein:

FIG. 1 is a diagrammatic view of a Mobile Offshore Production Storageand Offloading Unit (MOPSU) platform with caisson according to thepreferred embodiment of the present invention;

FIG. 2 is a diagrammatic view of the MOPSU platform with conductorsaccording to the preferred embodiment of the present invention;

FIG. 3 is a cross-sectional view of the MOPSU platform with conductors;

FIG. 4 is a top view of the hull with the conductors;

FIG. 5 is a top view of the mat with the conductors; and

FIG. 6 is cross-sectional view of the connecting legs connected to themat.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to a mobile offshore oil drilling andproduction platform. A detailed description of preferred embodiments ofthe invention is disclosed herein. It should be understood, however,that the disclosed preferred embodiments are merely exemplary of theinvention, which may be embodied in various forms. Therefore, thedetails disclosed herein are not to be interpreted as limiting, butmerely as the basis for the claims and for teaching one skilled in theart of the invention.

Generally, the present invention relates to a mobile offshore oildrilling, production and storage platform that allows a field operatorto cope with uncertainty and economically develop a small or marginaloil field typically located in a remote location. More particularly, theinvention relates to a versatile platform which includes a hullextending above the level of sea to house hydrocarbon extracting andscale up or scale down hydrocarbon processing system modules andequipment with provisions to drill new wells and work-overs usingmodular portable vertical drilling rigs or conventional rigs, connectedto a mat acting as the foundation resting on the seabed which may or maynot incorporate storage, using tubular legs, and provision to evenabandon the field with minimal costs and disruption.

The present invention also relates to a method of installing andde-installing the oil drilling, production and storage platform.

The present invention provides a Mobile Offshore Production Storage andOffloading Unit (MOPSU) platform and seeks to overcome the challengesand uncertainties surrounding small and marginal field developments. Thepresent invention also eliminates the need for a FSO vessel by providingstorage facility as an integrated feature of a mat.

As described briefly earlier, FIG. 1 is a diagrammatic view of a MobileOffshore Production Storage and Offloading Unit (MOPSU) platform withcaisson according to the preferred embodiment of the present invention,FIG. 2 is a diagrammatic view of the MOPSU platform with conductorsaccording to the preferred embodiment of the present invention, FIG. 3is a cross-sectional view of the MOPSU platform with conductors, FIG. 4is a top view of the hull with the conductors, FIG. 5 is a top view ofthe mat with the conductors and FIG. 6 is cross-sectional view of theconnecting legs connected to the mat. These drawings will be referred toindividually and collectively in the following detailed description ofthe preferred embodiment of the present invention.

As illustrated in the drawings, the MOPSU platform includes a hull (12)and a mat (14). The hull (12) and the mat (14) are connectable with legs(16).

Generally, the hull (12) includes facilities for drilling and processinghydrocarbons, accommodation quarters, offices and other facilities.

The legs (16) penetrate into the mat (14) and transfer the load througha reticulated network of stiffeners. This enables the mat (14) to takethe load from topsides through the legs (16) to the sea bed. The matcomprises a minimum of one ballast chamber (20), each connectable to oneterminal end region of each connecting leg (16) upstanding from theballast chamber (20) to above the hull. The ballast chamber (20) isintegrated to form a steel mat which will be used for stability duringtowing of the MOPSU. Once at installation site, the mat (14) is loweredby ballasting and strand-jacking until it reaches the seabed. The mat(14) is then fully ballasted to allow it to sink into the seabed toattain equilibrium. The mat (14) will then serve as the foundation forthe MOPSU, supporting the legs (16) and the facilities on the hull (12).

The present invention preferably includes four ballast chambers (20) andfour connecting legs (16). The ballast chambers (20) are connected viapiping rings and any one chamber can be by-passed or switched withanother by operating the valves on the piping rings. The connectingmeans used are known in prior art and will not be described herein.

The ballast chambers (20) preferably should include at least one oilstorage compartment, at least one air pressure compartment and at leastone ballast compartment. The ballasting and de-ballasting operations canbe performed by water/air and air/water displacement methods,respectively.

For ballasting, the air pressure compartment will be filled with water.When there is a need for de-ballasting, compressed air will be producedand channeled through the pipes to displace the water. The ballastchambers (20) are fitted with appropriate sensors for monitoring of theballasting and de-ballasting processes. The oil storage compartment isfor storing separated and stabilized crude oil. Extracted oil from theoil wells is transported to the hull for separation and stabilizationprocesses. After that, the oil is transported to the mat (14) and storedin the oil storage compartment. The oil is then offloaded to a shuttletanker via hoses on a periodic basis. The primary function of the legs(16) is to support the hull (12). Here, the legs (16) can also be usedas conduits for piping, umbilical and cables between the hull (12) andthe mat (14).

The MOPSU supports three different types of drilling systems. Inaddition to the provision of a wellhead deck for jack-up drilling, thehull (12) is designed to withstand loads imposed by tender assisteddrilling rig and self-erecting modular drilling rig. Self-erectingdrilling rigs, e.g. DrillTech produced by Streicher Group, are commonlyused for onshore drilling works. However, these can be marinised andcertified for offshore use. The entire drilling package can bemodularized into six modules with each module the size of a 12.2 m (40′)container.

The use of the portable modular drilling rig eliminates the need forexpensive jack up and self erecting drilling rigs. Once drilling hasbeen completed, the modules are removed and replaced by hydrocarbonprocessing systems and equipment. The hydrocarbon processing systems andequipment is constructed in the form of compact modules that are easilyhandled, tested and integrated prior to being shipped to their offshorelocation. The hydrocarbon processing systems and equipment provide astage by stage “building block” method of field development. As eachmodular processing unit is an integrated autonomous unit, it enablestotal integration testing to be undertaken in factory before deployment,thus increasing reliability and reducing installation and commissioningtime.

The modular processing units, may be of the general type forming part ofmodular system for sub-sea use designed by Alpha Thames limited ofEssex, United Kingdom, and referred to as AlphaPRIME. The modularprocessing units can be of two-phase and/or three-phase separationmodule and a booster pump with single well flow measurement. The modularprocessing unit for separation fluid mixtures is described in EP1555387. Furthermore, the modular processing unit can accommodate sandremoval as described in WO 03/041838 A1 and possibly a gas compressor.In fact, due to the AlphaPRIME system-modular design approach, any newtechnology can be included into an existing system at a later date, whenit becomes available, whilst production continues uninterrupted. Themodular processing unit can be progressively exchanged in the same way,in order to re-configure in response to changes of field characteristicsor in order to incorporate the latest technology for optimum production.

A self-installing drilling template (22) which can be removeablyattached to be a stand-alone wellhead platform has been added to theMOPSU as an enhanced feature. The self-installing drilling template ismade up of a wellhead deck (24) removeably attached to the hull (12) ofthe MOPSU and a caisson subsea clamp or a conductor subsea support frame(32) removeably attached to the mat (14) of the MOPSU.

The self-installing drilling template (22) is to be used to supportconductors (26) or a caisson (28) containing drilling casings. A caisson(28) can be pre-installed onto the MOPSU at the fabrication site andtowed to the offshore site together with the MOPSU. The caisson (28) isclamped at the mat (14) and secured at the wellhead deck (24) duringtow. Alternatively, instead of pre-installing a drilling caisson (28)onto the MOPSU, drilling conductors (26) can be driven or drilledthrough the drilling template (22), and casings run inside the drillingconductors (26) instead of the caisson (28). The MOPSU platform supportsboth the above options for drilling template.

The MOPSU is self-installing and thus the timing for installation andde-installation does not have to coincide with availability of a derrickbarge or a jack-up drilling rig.

The method of installing the MOPSU is now described. The MOPSU,comprising of the hull (12), mat (14), legs (16), caisson (28), wellheaddeck (24) and sub-sea support clamp (for MOPSU with caisson)/frame (32)(for MOPSU with conductors), is constructed and assembled at afabrication yard and its quayside before towing to an offshoreinstallation site as an integrated unit.

Once the MOPSU is assembled and ready for the tow, strand jacks areinstalled and the ballast levels in the hull (12) and the mat's ballastchambers are adjusted to achieve the required draft and trim for the towto offshore installation site. Then the legs (16), caisson (28), flaretower, etc. are secured for the tow by sea-fastening. The fullyassembled MOPSU is then towed by one or two tugs. Upon reaching thedestination, the sea-fastening is removed and ballast levels adjusted toachieve even trim. The strand jacks are then activated and ballastingcommences to lower the mat (14), legs (16) and the caisson (28) to theseabed. All the ballast chambers (20) in the mat (14) are then fullyballasted to allow the mat (14) to sink. Once the mat (14) sinks intothe seabed to achieve equilibrium, the sub-sea clamp holding the caisson(28) is released to allow the caisson (28) to self-penetrate into thesoil until it becomes self-standing. The sub-sea clamp will then bere-activated to provide lateral support for the caisson (28).

The hull (12) is then fully de-ballasted and jacked-up to the desiredheight to provide adequate air gap. The strand jacks are thendeactivated and disconnected for use at another MOPSU. The platform isthen secured and prepared for drilling activities to extracthydrocarbons from the target reservoirs.

The extracted hydrocarbons are transported to the hull (12) forseparation and stabilization before storing the crude oil in the mat.When all the oil compartments fill-up, a shuttle tanker is mobilized andthe crude oil is offloaded using hoses.

The method of de-installing the MOPSU will now be described. Afterdrilling and production operations, the wellhead deck (24) can besecured to the drilling caisson (28) by way of welding or any othersecuring means and is then detached from the hull (14). The sub-seaclamp will then be de-activated and the MOPSU de-installed to leave theoffshore site. The caisson (28) will then be self-standing andsupporting the wellhead deck (24) for further well intervention andworkovers. Where conductors (26) are used instead of the caisson (28),after drilling and production operations, the wellhead deck (24) can bewelded to the conductors (26) and detached from the hull (12). The guideframe at the mat (14) can similarly be released and the MOPSU can bede-installed to leave the conductors free-standing to support the hull(12).

The de-installation of the MOPSU is essentially a reverse of theinstallation procedure. However, before the de-ballasting can takeplace, water jets will have to be used to break-out the consolidatedclay layer below the mat (14). Strand jacks are then activated and themat (14) and legs (16) jacked-up. The hull (12) is then jacked down tosea level, draft and trim adjusted and tug (s) connected for the tow tothe next destination.

The caisson (28) or conductors (26) that support the wellhead deck (24)will then be stand-alone for further well intervention and workovers orabandonment. Further production can be planned with much highercertainty based on the performance achieved via the MOPSU.

The MOPSU clearly from the descriptions above offers total flexibilityat optimal cost by providing drilling to be carried out and uponcompletion allowing hydrocarbon processing to be carried out with thestabilized crude stored in the integrated storage tanks, all by the sameunit. The self installing drilling template further offers scaling up orcost effective abandonment with the MOPSU deployed elsewhere.

1. A mobile offshore oil drilling and production platform (10) whereinthe platform includes: (a) a hull (12); and (b) a mat (14), wherein themat (14) is connected to at least one connecting leg (16) substantiallyvertical upstanding from the mat (14) to the hull (12) and the mat (14)includes at least one ballast compartment to be filled with sea water orcompressed air in the platform; characterized in that: a drillingtemplate (22) attached to the hull (12) and mat (14) by connecting meanswherein a drilling template (22) is removeably attached to the hull (12)and mat (14); and the at least one connecting leg (16) is provided withat least a stiffener, wherein the load of the platform (10) istransferred over a substantially large area of the mat (14), then toseabed.
 2. The platform as claimed in claim 1, wherein the platform (10)includes storage facilities.
 3. The platform as claimed in claim 2,wherein the mat (14) includes at least one ballast compartment (20) forstoring processed oil.
 4. The platform as claimed in claim 1, whereinthe drilling template (22) consists of a wellhead deck (24) that isremoveably attached to the hull (12) and a subsea clamp or a removablyattached conductor (26) subsea support frame (32) that is attached tothe mat (14).
 5. The platform as claimed in claim 1 wherein the drillingtemplate (22) supports conductors (26) or a caisson (28) to containdrilling casings.
 6. The platform as claimed in claim 5 wherein thecaisson (28) is pre-installed by clamping it to the mat (14) andsecuring it to the wellhead deck (24) during towing of the platform. 7.The platform as claimed in claim 1 wherein the platform (10) isrelocated to a different location without the drilling template (22)after the completion of the drilling process.
 8. The platform as claimedin claim 1 wherein the platform (10) is attachable to another drillingtemplate (22) or a wellhead platform at a different location.
 9. Theplatform as claimed in any one of the preceding claims, wherein theplatform (10) is constructed and fully assembled at a fabrication yardand its quayside before towing to an offshore installation site as anintegrated unit.
 10. A method of installing a mobile offshore oildrilling and production platform (10) as claimed in claim 9, wherein themethod includes the steps of: (a) adjusting ballast levels in the hull(12) and the mat's ballast chambers to achieve all required conditionsfor the platform to be towed to an offshore installation site; (b)securing parts of the platform such as the legs (16) and caisson (28) bysecuring means such as sea-fastening for the tow; (c) towing theplatform to the site; (d) removing the securing means such asseafastening; (e) adjusting the ballast levels to achieve all requiredconditions; (f) activating the heightening means so that the mat (14),legs (16) and the caisson (28) or the conductor subsea support frame(32) to be lowered from underneath the hull (14) to the seabed; (g)de-activating a subsea clamp holding the caisson to the mat (14), toallow the caisson (28) to self-penetrate; (h) re-activating the clamp toprovide lateral support for the caisson (28); (i) fully de-ballastingthe hull (12); and (j) activating the heightening means to elevate thehull (12) to a desired height.
 11. The method as claimed in claim 10,wherein the platform (10) includes storage facilities.
 12. The method asclaimed in claim 11, wherein the mat (14) includes at least one ballastcompartment (20) for storing processed oil.
 13. The method as claimed inclaim 10, wherein the extracted hydrocarbons are transported to the hull(12) for separation and stabilization.
 14. The method as claimed inclaims 12 and 13, wherein the processed oil is transported to the mat(14) and stored in the at least one oil storage compartment.
 15. Themethod as claimed in claim 14, wherein when the at least one oil storagecompartment is full of the processed oil, a shuttle tanker is mobilizedand the processed oil is offloaded using transporting means such ashoses.
 16. A method of de-installing a mobile offshore oil productionand processing platform (10) which has been installed according to amethod as claimed in claim 10, wherein the method of de-installingincludes the steps of: (a) securing the wellhead deck (24) to thecaisson (28) or conductors (26) by a securing means; (b) detaching thedrilling template (22) from the hull (12); (c) de-activating a subseaclamp holding the caisson (28) or the securing means to release thesubsea support frame from the mat (14); (d) activating the heighteningmeans so that the hull (12) is lowered to substantially the sea level;(e) removing any adhesion caused by soil-in areas surrounding the mat;(f) activating the heightening means so that the mat (14) and the legsare returned from the sea-bed to underneath the floating hull (12); and(g) re-adjusting the platform to required conditions for towing to thenext destination.
 17. The method as claimed in claim 15, wherein theplatform (10) includes storage facilities.
 18. The method as claimed inclaim 16, wherein the mat (14) includes at least one ballast compartment(20) for storing processed oil.